Due to continuing reductions in dimensions of portable communication equipment, there is a need in the art for improved electroacoustic transducers such as miniature loudspeakers or receivers that provide improved vibration performance and superior sound pressure output capability in a small package.
US 2003/0048920 A1 discloses a miniature dual-diaphragm electro-dynamic loudspeaker that comprises a magnet system disposed between a pair of oppositely positioned parallel diaphragms. A unidirectional magnetic flux is created within each of two unidirectional magnetic gaps by an associated magnet. A separate magnetic flux path extends around each of the magnetic gaps and its associated magnet in a plane substantially parallel to the oppositely positioned parallel diaphragms. Due to the unidirectional property of the magnetic flux in each magnetic gap both conductive coils are folded. While the disclosed miniature transducer has a number of noticeable advantages such as very small height, the need for folded conductive coils and separate magnetic flux paths around each unidirectional gap may render the disclosed transducer with less than optimal conversion efficiency. Conversion efficiency and size constraints are generally important performance measures of electroacoustic transducers, in particular for portable communication equipment like single cell driven devices such as hearing instruments.
U.S. Pat. No. 6,622,817 discloses a dual-panel loudspeaker working according to a bending wave principle comprising a motor structure with a common magnetic flux path. Two oppositely positioned and parallel sound panels are operable to overcome acoustic short circuiting between front and rear side sound radiation of a traditional single panel loudspeaker where front and rear sound radiation are out of phase.
A miniature electroacoustic transducer according to the present invention is particularly well-adapted for use in battery powered portable devices such as mobile terminals and hearing instruments and provides improved performance to one or several key performance measures such as cost, vibration output level, acoustical conversion efficiency, maximum sound pressure capability and package size.